1. Field of the Invention
This invention relates generally to information record discs employing a flexible magnetic sheet material as the record medium, and more particularly is directed to improvements in the hub structure of such flexible magnetic discs.
2. Description of the Prior Art
It has been proposed to employ a flexible magnetic disc, preferably rotatable within a flat cassette casing, for recording video or other signals in a series of concentric, circular tracks, on a flexible magnetic sheet member of the disc which further includes a hub structure secured to the center of the sheet member. The hub structure of the magnetic disc defines a bore for receiving a drive spindle of a recording and/or reproducing apparatus by which the flexible magnetic disc is rotated during recording or reproducing of the information signals by means of a magnetic head scanning the respective circular track on the flexible magnetic sheet member. In order to minimize the diameter of the disc and still provide for the recording on the disc of a substantial quantity of video or other information, it is necessary to employ high density recording with minimum if any clearances between the adjacent tracks. Such high density recording requires the avoidance of disc eccentricity, particularly when various discs are interchanged with each other or employed in different recording and/or reproducing apparatus.
In a proposed flexible magnetic disc of the above-described type, the hub structure is molded of a synthetic resin and is formed, within the bore which receives the drive spindle, with oppositely angled positioning surfaces which converge in the direction away from the center or axis of the bore, and further with one or more resilient tabs or members molded as integral parts of the hub structure at a side of the bore remote from the positioning surfaces and engageable with the drive spindle in the bore for securely seating the drive spindle against the positioning surfaces. However, the foregoing arrangement is not completely satisfactory in avoiding disc eccentricity in that, by reason of the molding of the positioning surfaces and resilient tabs or member as integral parts of the hub structure formed of a synthetic resin, the dimensions and relative positions of such elements provided for locating the center of the flexible magnetic disc in respect to the axis of rotation of the drive spindle may vary from one disc to another and with time. Further, the spring force with which the resilient tabs or member molded integrally with the hub structre are effective to press the drive spindle against the positioning surfaces is also variable due to dimensional variations of these parts as molded and with time, for example, due to wearing away of the resilient tabs or member or the positioning surfaces with repeated use of the flexible magnetic disc.